In radio communication systems for mobile telephones and the like, communication is performed by using signals that are obtained by quadrature-modulating (IQ modulating) channel-coded, coded bits, using PSK (Phase Shift Keying), QAM (Quadrature Amplitude Modulation), etc.
FIG. 25 is one example of a receiver apparatus that receives a quadrature-modulated signal in single-carrier transmission. A receiver apparatus 900 includes a low-noise amplifier 902 (LNA: Low Noise Amplifier), a frequency converter 903, a filter unit 904, a gain control amplifier 905, an IQ detector 906, an AD converter 907, a demodulator 908 and a decoder 909, and is connected to an antenna unit 901.
In receiver apparatus 900, the quadrature-modulated signal received via antenna unit 901 is amplified by low-noise amplifier 902, then down-converted by frequency converter 903 to an IQ-detectable frequency band. The output signal from the frequency converter 903, from which higher harmonics and the out-of-band components of the signal are removed by filter unit 904, and then is adjusted as to amplitude so that the signal will not be clipped by IQ detector 906 and AD converter 907.
In IQ detector 906, the in-phase component (real number component) and quadrature component (imaginary number component) are extracted from the output signal of gain control amplifier 905. In AD converter 907, the signals of the in-phase component and quadrature component are each converted from an analog signal to a digital signal. In demodulator 908, the digital signals of the in-phase component and quadrature component output from AD converter 907 are demapped so as to calculate coded bits. Finally, a decoding process of the coded bits is performed by decoder 909.
In the above receiver apparatus 900, low-noise amplifier 902, frequency converter 903, filter unit 904, gain control amplifier 905 and IQ detector 906 are formed of analog circuitry while demodulator 908 and decoder 909 are formed of digital circuitry, and AD converter 907 performs conversion.
In the analog circuit of the above receiver apparatus 900, in order to decode data with high precision, it is necessary to keep linearity when the processes from amplication of the quadrature-modulated wave, extraction of in-phase and quadrature components and input to the demapping process are performed. In other words, in order to reproduce the signal waveform with as less deformation as possible, an analog circuit having a wide dynamic range in which good linearity is maintained up to input to AD converter 907 is needed. Further, AD converter 907 needs to have a voltage resolution that satisfies the quantization error absorbable by the digital process. It is necessary for gain control amplifier 905 to perform highly accurate gain control over a wide range so that the signal will not be clipped by the AD converter 907
On the other hand, in radio communication systems such as mobile telephones etc., it is preferable that the receiver apparatus is compact and low in power consumption, so that there are integrated ICs in which the analog circuit and digital circuit that form the receiver apparatus are integrated (see non-patent document 1, for example). It is possible in the integrated IC to achieve reduction in IC chip size and high-speed operation with low voltage thanks to miniaturization of devices, hence it is possible to make the receiver apparatus compact and low in power consumption. Non-patent document 1 presents an IC design example where analog circuits and digital circuits for the portions having the corresponding functions are integrated though the order of arrangement of individual functional components is different from that of the receiver apparatus 900.